There has been known an optical module having a semiconductor element such as large scale integration (LSI) mounted on a mounting board such as a silicon substrate mounted with an optical waveguide, in addition to an optical element such as a light receiving element or a light emitting element. For example, there has been known an optical module, in which an LSI onto which a light receiving element is bonded via a solder bump is bonded onto a silicon substrate via a solder bump in the state in which the light receiving element is disposed in a recessed portion of the silicon substrate mounted with an optical waveguide.
When the mounting board mounted with the optical waveguide is mounted on a separate board and connected to the separate board by a wire in order to supply electrical signals to the semiconductor element on the mounting board mounted with the optical waveguide, a wiring length reaching the semiconductor element on the mounting board is increased, and as a result, a high-speed operation of the optical module may not be achieved.
The followings are reference documents.    [Document 1] Japanese Laid-Open Patent Publication No. 2000-352643, and    [Document 2] Akinori Hayakawa etc., “A 25 Gbps silicon photonic transmitter and receiver with a bridge structure for CPU interconnects”, Optical Fiber Communication Conference 2015 Los Angeles, Calif. United States 22-26 March 2015.